(Reuters) - Actor Philip Seymour Hoffman, who won an Academy Award for the film "Capote," was found dead in his New York City apartment on Sunday in what a police source described as an apparent drug overdose.

Hoffman, 46, was found unresponsive on the bathroom floor of his Greenwich Village apartment by police responding to an emergency 911 call, and Emergency Medical Service workers declared him dead on the scene, the New York City Police Department said in a statement. An investigation was ongoing.

TheNew York Times, citing a law enforcement official, said investigators found a syringe in Hoffman's arm and an envelope containing what was believed to be heroin.

A police department source told Reuters that Hoffman had died of an apparent drug overdose.

Hoffman, who is survived by three children with his partner Mimi O'Donnell, had detailed his struggles with substance abuse in the past.

"We are devastated by the loss of our beloved Phil and appreciate the outpouring of love and support we have received from everyone," Hoffman's family said in a statement issued through his publicist on Sunday afternoon.

"This is a tragic and sudden loss and we ask that you respect our privacy during this time of grieving. Please keep Phil in your thoughts and prayers," it added. A representative said the family would not make any further statements at this time.

Born in upstate New York near Rochester, Hoffman won the best actor Oscar for the 2005 biographical film Capote, in which he played writer Truman Capote. He also received three Academy Award nominations as best supporting actor, for The Master in 2013, Doubt in 2009 and Charlie Wilson's War in 2008.

After more than a dozen earlier roles, Hoffman burst onto the film scene in 1997's Boogie Nights, in which he played a lovelorn gay man, in the movie about the porn industry that helped make Mark Wahlberg a star.

Hoffman appeared in blockbusters such as Twister and The Hunger Games series. But he was more often associated with the independent film world for his intense portrayals of often disturbing and complex characters in such films as Happiness, in which he played an obscene phone caller, and Before the Devil Knows You're Dead.

In the latter, he played a son who schemes to rob his parents' jewelry store, resulting in their deaths. But Hoffman could also play nice, as in Magnolia, in which he played the role of an angelic nurse.

Other noteworthy films included Moneyball, The Savages, Cold Mountain and Scent of a Woman, one of his earliest films, for which Al Pacino won an Oscar.

Hoffman also frequently appeared on Broadway, garnering Tony award nominations for Death of a Salesman, Long Day's Journey Into Night and True West.

Hoffman spoke in the past of struggling with drugs, including a 2006 interview in which he told CBS he had abused "anything I could get my hands on. I liked it all."

New York Mayor Bill de Blasio said via Twitter: "Saddened by Philip Seymour Hoffman's tragic and untimely passing. Today New York mourns the loss of one of stage and screen's greats."